Infra-red gas analyzing apparatus



July 29, 1952 A. E. MARTIN INFRA-RED GAS ANALYZING APPARATUS Filed OCT.. 1. 1949 M y M p m r A M m t A T m p m L9 M A M p W G 5 A 5 J 5 4 A Patented July 29, 1 952 2.60pm 1 INFItA-RED GAS ANALYZING,

Albert E. Martin, Newcastle are as. sigma, assignor to C. A. Parsons & Company Limited, Newcastle upon Tyne, England Application October 1, 1949, Serial No. 119,038 In Great Britain October 6, 1948 2 Claims. 1

drawing, there is provided one long tube B and a second tube separated into three tubes B1, B2, B3 of difierent lengths. Windows G are furnished which are pervious to radiations emitted by the heaters A. Two nichrome heaters A and a rotary perforated disc F are also provided.

Detector chambers C and C1 define a space which is separated into two portions by a flexible partition D, adjacent to which is positioned an duced and any difference between the two chambers causes the diaphragm to deform and so give rise to changes of capacity in respect of an insulated perforated metal plate which is fixed in close proximity to the diaphragm.

If both gas tubes contain gas with no infrared absorption and the radiation from the heaters is interrupted by a rotating shutter which admits light simultaneously to the tubes, the pressure pulses in the two chambers will balance and no movement of the diaphragm will result; but if some of the gas to be detected is passed into one of the absorption tubes, energy will be absorbed before it can reach the corresponding detecting chamber. The balance will now be upset and the diaphragm will vibrate at the frequency of interruption of the radiation.

The capacity changes are amplified electronically and finally an indication is obtained on a meter which can be calibrated in gas concentration.

This instrument essentially measures only the particular gas which is contained in the detecting chambers, since other gases will not absorb the wavelengths which are effective in heating the gas in the detecting chambers.

The object of the present invention is greatly to extend the range of the instrument.

The invention consists in brief in an infrared gas analyser of the kind set forth above wherein radiations are passed through .a succession of tubes of varying length in place of the single absorption tube usually employed, the particular tube appropriate to the concentration range required being used to contain the sample gas and the other or others being filled with dry CO2 free air or a filtering as when necessary.

The invention also consists in infra-red gas analysers substantially as described.

The accompanying diagrammatic drawing i1- lustrates an infra-red gas analyser constructed in one form in accordance with the present invention.

In carrying the invention into effect according to one example illustrated in the accompanying insulated perforated metal plate E, so that the deformation of the diaphragm D in response to cause changes in the capacity of the diaphragm D with respect to the plate E. These capacity changes may be amplified electronically and finally furnish an indication on a meter calibrated in terms of gas concentration.

If a low concentration of gas is to be measured, the tube B is filled with dry CO2 free air and the gas sample is passed through the tube E1, the other tubes B2 and B3 being filled with dry CO2 free air and sealed off. At higher concentrations the absorption occurring in the pathlength of the tube B1 is so great that saturation is approached and increasing concentration gives less and less extra absorption. At this stage the tube B2 is put into use for the sample gas and tubes B1 and B3 are filled with dry CO2 free air and sealed off. A much higher concentration can now be measuredand when the absorption in this tube becomes too great, the shortest tube B3 can be used, the other two tubes B1 and B2 being filled with dry CO2 free air.

The guiding principle is that concentration multiplied by tube length should not exceed a certain value depending on the gas in question,

if a reasonably linear calibration curve is re-,

quired. I

Instead of filling the tubes not required for I into two portions by a flexible partition, a wina 3 similar windowed gas chambers of relatively different lengths disposed in line between the other of said chamber windows and the other of said the concentration of which is to'be measured and the other or another of said tubes is filled m with a gas serving as a filter.

REFERENCES CITED The following references are of record in the file of this :patent:

UNITED STATES PATENTS Number 7 Date $431,019 f New. I8, 1947 2443,42?" Juri'e-l5, 1948 2,451,572

Moore Oct. 19, 1948 

